1. Field of the Invention
The invention relates generally to an annulus shutoff valve. More particularly, the present invention relates to an annulus shutoff valve that seals one or more annulus flowby ports. Still more particularly, the present invention relates to a subsea tubing hanger with an integral annulus shutoff valve, which seals one or more annulus flowby ports in the tubing hanger, and is employed to safely close off or isolate an annular space below the tubing hanger.
2. Background of the Invention
In general, valves are devices used to regulate the flow of fluids (e.g., gases, liquids, slurries, etc.) through a passage by opening, closing, or partially obstructing the passage. Valves are used in hundreds of industrial, military, commercial, and even residential applications. Depending on the application, the failure of a valve may potentially result in undesirable consequences such as damage to the system of which the valve is a part, an inability to regulate fluid flow through the valve, and significant repair and downtime expenses.
A common type of valve is a piston-cylinder valve having a piston slidingly disposed within the inner cavity or central bore of a cylinder. Often, an annular seal, which may be seated in a groove around the piston, is provided between the piston and the inside surface of the cylinder wall. By sealingly engaging the inside surface of the cylinder wall, the annular seal prevents the flow of fluids across the piston between the piston and cylinder wall. In addition, an inlet port and an axially spaced apart outlet port are typically provided through the cylinder wall. When the piston is positioned between the inlet port and the outlet port, the piston prevents fluid communication between the inlet port and the outlet port, thereby placing the valve in a “closed” position (e.g., the piston and annular seals block the flow of fluid from the inlet port, through the cylinder cavity, to the outlet port). However, if the piston is not axially positioned between the inlet port and the outlet port, fluid communication between the inlet port and the outlet port is permitted, thereby placing the valve in the “opened” position (e.g., the piston does not block the flow of fluid from the inlet port, through the cylinder cavity, to the outlet port).
In many conventional piston-cylinder valves, a hydraulic or pneumatic actuator is employed to control the movement of the piston within the cylinder, thereby controlling the status of the valve as “opened” or “closed.” As the piston is moved between the inlet port and outlet port, or outside the inlet port and outlet port, the piston, and any annular seals around the piston, may cross over one or both ports.
Piston-cylinder valves may be utilized to divert fluid flow in oil or gas production dual-bore wellhead assemblies. For instance, in a subsea oil or gas production well, the wellhead assembly typically includes a tubing hanger having a vertical production bore and at least one vertical annulus bore that is in fluid communication with a tubing annulus and is located below the tubing hanger and between the production tubing and the production casing. In dual-bore wellhead assemblies, two plugs may be required to separately shut off or regulate the flow of fluids into or from the annulus bore, and to shut off the production bore in order to abandon the well or to remove a blow-out preventer (BOP) stack. The running of two separate plugs results in additional equipment and operating costs and time, and decreases the operational flexibility of wellhead assemblies characterized by this dual-bore configuration.
A piston-cylinder valve with typical annular seals that is known in the art may be used to control access to the vertical annulus bore, or tubing annulus, and to regulate the flow of fluids into or from the annulus through the tubing hanger. Valves of this type are typically not integral to the downhole equipment they are intended to serve, and as a result are not easily installed, accessed, removed or replaced. As such, the installation or removal of these non-integral valves may require the removal of conflicting upstream wellhead equipment, thereby disturbing wellhead operations. Further, the failure of the annular seal in the piston-cylinder valve may require a shutdown of the producing well, and necessitate accessing the piston-cylinder valve by removing upstream equipment such as a Christmas tree or a BOP, pulling the valve from the tubing hanger, and repairing or replacing the valve. A leaking valve or inoperable valve resulting from damage may require replacement or repairs, potentially resulting in significant maintenance costs and downtime. In addition to significant well downtime, such a procedure may result in increased associated cost, such as well as repair and maintenance expenses to access, pull, and repair or replace the failing valve.
Thus, there remains a need to develop methods and apparatus for more flexible wellhead assembly with integral annulus valve configurations, as well as more easily accessible piston-cylinder valve assemblies that overcome some of the foregoing difficulties while providing more advantageous overall results.